Appendix to Chapter V. 439 
the burden of proof is thrown upon those who point to par- 
ticular cases where there is thus a conspicuous absence of 
transitional forms—the burden, namely, of proving that such 
cases are not due merely to a break in the record. Besides, 
the break in the record as regards this particular case may 
be apparent rather than real. For I suppose there is no 
greater authority on the pure geology of the subject than 
Sir Charles Lyell, and this is what he says of the particular 
case in question. “If the passage seem at present to be 
somewhat sudden from the flora of the Lower or Neocomian 
to that of the Upper Cretaceous period, the abruptness of 
the change will probably disappear when we are better ac- 
quainted with the fossil vegetation of the uppermost tracts of 
the Neocomian and that of the lowest strata of the Gault, or 
true Cretaceous series 1.” 
Lastly, the fact of the flora of the glacial epoch not 
having exhibited any modifications during the long residence 
of some of its specific types in Great Britain and else- 
where, is a fact of some importance to the general theory of 
evolution, since it shows a higher degree of stability on the 
part of these specific types than might perhaps have been ex- 
pected, supposing the theory to be true. But I do not see that 
this constitutes a difficulty against the theory, when we have so 
many other cases of proved transmutation to set against it. 
For instance, not to go further afield than this very glacial 
flora itself, it will be remembered that in an earlier chapter 
I selected it as furnishing specially cogent proof of the 
transmutation of species. What, then, is the explanation of 
so extraordinary a difference between Mr. Carruthers’ views 
and my own upon this point? I believe the explanation to 
be that he does not take a sufficiently wide survey of the 
facts. 
To begin with, it seems to me that he exaggerates the 
vicissitudes to which the species of plants that he calls into 
1 Elements of Geology, p. 280. 
